(1) Field of the Invention
The present invention generally relates to an interior structure of an input device, which comprises at least one input unit, and particularly to a touching rib of the input unit.
(2) Description of the Prior Art
Among many kinds of electronic devices, an input device is needed for operating these device or for inputting commands or information into these devices. For example, input device such as keyboard comprises many keys. These keys are the mentioned input units. Typically, the input unit comprises a touching rib for touching an electronic switch of a electronic device.
Please refer to FIG. 1. FIG. 1 shows the bottom of a prior input unit 2. The input unit 2 comprises a pressing portion 3 and a touching rib 4. The pressing portion 3 comprises a top face 31 and a bottom face 32. The touching rib 4 is disposed on the bottom face 32. An user can press the top face 31 of the input unit 2 so as to touch an electronic switch (not shown) of an electronic device by the touching rib 4. The electronic switch is usually electrically connected with a circuit of the electronic device. For example, some typical electronic switch is directly mounted on a printed circuit board (PCB) and electrically connected with it.
As to the fabrication method of the prior input unit 2, a mold 10 shown in FIG. 2 is utilized for filling plastic materials to form the input unit 2. The mold 10 has a cavity 12 corresponding to the shape of the input unit 2. The cavity 12 can be divided into a first portion 13 and a second portion 14, which have corresponding shapes to the pressing portion 3 and the touching rib 4, respectively. As shown in FIG. 2, the second portion 14 of the cavity 12 has a shape of cross corresponding to the touching rib 4 shown in FIG. 1.
In one typical prior art, the whole cavity 12 is formed by an electric discharge machining (EDM) process toward the material of the mold 10. Hence, the cavity 12 is airtight except for the opening for filling the plastic materials. While filling the plastic materials of the input unit 2 into the cavity 12, bubbles may be formed at the interface between the mold 10 and the plastic materials. If these bubbles are formed at the bottom of the second portion 14 of the cavity 12, it may cause the formed touching rib 4 shorter than a predetermined height. In some worse situation, the shortened touching rib 4 is not able to touch the electronic switch and loses its predetermined function.
Please refer to FIG. 3. FIG. 3 shows another prior mold for fabricating the input unit. For resolving the mentioned problem of bubbles, another prior mold 20 is provided. The second portion 24 of the cavity 22, which is needed for forming the touching rib 4, is ventilative in this prior art. While filling the plastic materials of the input unit 2 into the cavity 22, an inlay 26 is disposed at the bottom of the second portion 24 of the cavity 22 to jointing with the mold 20. There is a plurality of micro-chinks between the inlay 26 and the mold 20 so as to allow air, which is formed between the plastic materials of the input unit 2 and the inlay 26, to flow out. By this inlay 26, the mention problems of bubbles and the shortened touching rib 4 is somehow resolved.
However, another problem is aroused because of using the inlay 26. While filling plastic materials into the cavity 22 shown in FIG. 3, not only air can flow through the micro-chinks between the inlay 26 and the mold 20, some plastic materials flow into these micro-chinks either. Although the amount of the plastic materials flowing into the micro-chinks is very limited, roughness structures such as fibers can readily be formed on the surface of the touching rib 4. The roughness surface or a too long height may frustrate the predetermined function of the touching rib 4.
As described above, while the input unit is elementary to many kinds of input devices. An input unit without the foregoing drawbacks is therefore needed. There are demands to provide a method for fabricating a input unit comprising a touching rib with a smooth surface and an accurate height corresponding to its predetermined design.